1. Field of the Invention
The invention is generally related to instrumentation methods for monitoring and measuring fatigue in pipes or conduits for carrying cryogenic materials and is specifically directed to a pipeline system including fiber optic sensor instrumentation systems and methods.
2. Discussion of the Prior Art
Pipeline transfer of cryogenic fuels and other liquids such as liquid natural gas (LNG) is commonplace throughout the world. In fact, LNG is currently the fastest growing hydrocarbon fuel in the world. While gas as a primary fuel source is forecast to grow at 3% in the coming two decades, LNG is forecast to grow at double that rate over the same period. This growth will result in the need for additional facilities for the production and transportation of LNG in the foreseeable future, and as a result new technologies will emerge to address cost, safety and reliability issues that this expansion may create.
For example, LNG loading into the tankers and the offloading thereof, require the use of terminals designed to handle the LNG. Terminals at the loading site are normally close to the liquification plant and traditionally on the offloading end, and the terminal is typically situated near a storage facility and re-gasification plant. Proximity of the onshore terminals to water access has prompted a review of increased shipping traffic in congested waterways. As terminal siting concerns build over pressures from environmental and public safety issues, there is a trend to reconsider moving terminal locations offshore.
Given that both production and import of LNG will move more and more offshore, there is a growing need for a safe, efficient and reliable transfer system. Beginning in the 1970's, a sub sea LPG pipeline was designed for a Middle Eastern LPG terminal. This continued into the 1980's with the first sub sea LNG pipeline for an arctic LNG ship system in Alaska.
Terminals are required for both the loading of LNG into the tankers and for offloading thereof. For locations with sufficient deep water access close to the coast, terminals may consist of jetty structures and breakwaters, where tankers can be moored and offloading can take place via the standard loading arms.
When conditions are less favorable due to shallow waters, congested shipping and/or mooring situations, or because of lack of community acceptance and permitting difficulties, offshore terminals are a very attractive alternative. Although such terminals exist—they have been widely used for loading of crude oil and oil products for many years—no offshore terminals for LNG are in use.
The most dominant advantages of LNG offshore terminals are the lower costs for construction and operation, the possibility to locate the terminal in deeper water thereby eliminating the need for dredging and increased availability, safety and reduced voyage time as LNG carriers need not enter and maneuver in congested waters. LNG carrier berths can be located away from confined waterways, thereby increasing both safety and also security, while at the same time reducing costly civil works. Furthermore, impairment of other new and existing shipping traffic will be minimized.
A sub sea pipeline can be used to transport the LNG from/to an offshore terminal, thereby eliminating the need and cost for a connecting trestle. With current sub sea cryogenic pipeline designs, LNG can be efficiently transferred over distances of up to 20 miles.
Current pipeline technologies for cryogenic products, such as LNG, use both flexible hoses and rigid pipe. The former is limited to short-distance loading and offloading hoses because of the high expense and the limitation of insulation that can be provided. For longer distance pipelines, rigid pipelines must be used. Current configurations and methods for rigid cryogenic pipelines typically involve the use of low pressure or vacuum environments in an insulating space around a product pipeline to achieve the desired thermal performance characteristics. While low pressure or vacuum systems often provide relatively good insulation, operation and maintenance of such systems tends to be costly, and frequently becomes problematic where such pipelines are submerged on, or even below the sea bed.
Other difficulties are also often encountered, most typically associated with thermal expansion/contraction due to cooling, compression and/or structural stability. For example, one current technology accommodates the contraction by the use of INVAR (36% Nickel Steel), which has very low expansion and contraction properties. In such a configuration, the INVAR steel product transportation line is contained within an external steel casing pipeline with a partial vacuum on the insulated annulus. While thermal expansion is almost completely avoided, various disadvantages nevertheless remain. For example INVAR steel is relatively expensive and often cost prohibitive. Moreover, generation and maintenance of the low pressure (e.g., 100 mbar) in the pipeline assembly requires considerable energy and cost over the life of the pipeline.
In other known configurations, contraction and expansion capabilities are improved with the use of bellows. This configuration incorporates the use of bellows, one in each segment (about 50 ft long) of the pipeline, which is a self-contained pipe-in-pipe segment, and uses vacuum insulation. However, the use of bellows along the length of pipeline typically increases production costs, and typically complicates manufacture, handling and maintenance. The bellows methods are generally more costly than the INVAR™ system. The bellows method has significant disadvantages in reliability and durability, both with the bellows and with the maintenance of vacuum. For a sub sea application, reliability and durability are even more critical.